The present invention relates to a film data exposure device for exposing identification data such as the frame numbers, brand, emulsion number, bar code, side line, characters, and symbols as latent images on unexposed films in the production process of roll films for photographic cameras.
Hereafter in the specification, the identification data are referred to as "latent image data."
Some film data exposure devices for exposing latent image data to unexposed films as mentioned above use original negative films, and there are also some which do not use such negative films.
A film data exposure device using a negative film exposes latent image data to an unexposed film using transmitted light through the negative film. When setting the emulsion number, for example, unnecessary numbers of 0 to 9 are blacked out.
A film data exposure device using no negative film exposes latent image data on an unexposed film as follows: the unexposed film is fed at a predetermined speed, the latent image data to be exposed is stored in a memory beforehand, a position signal is generated in synchronization with the feed of the unexposed film and the latent image data is read out of memory to form latent images on the unexposed film.
When exposing latent image data on unexposed films with light through the negative films, different negative films same in number as production lines are required to be prepared according to the brand, emulsion number, size, and type symbol, causing a difficulty in reservation of the arrangement space. Furthermore, replacement of negative films requires a long time.
In a film data exposure device using no negative films, the latent image data to be exposed to unexposed films are set and stored in an exposure device beforehand for each unexposed film, and the latent image data is read and exposed to unexposed films synchronized with the feeding speed thereof. Therefore, there is no need to prepare negative films in the number of production lines.
The type of films, for example, may be changed or added. If this occurs, the brand is changed or added. When latent image data is often added or changed, however, there is a problem imposed such that a film data exposure device, which stores beforehand latent image data to be exposed for each unexposed film, cannot deal with changing or addition of latent image data simply and quickly.
Furthermore, when latent image data is often added or changed, the latent image data, which is actually exposed, is required to be confirmed immediately after it is changed. In the case of a conventional data exposure device, the alarm device functions only when an error occurs, and it takes a lot of time to check the entire contents of the latent image data which is being exposed because it is required to be developed for visual check.
When exposing latent image data in a conventional film data exposure device, an unexposed film is pulled out from the feed source and a notch is cut one side of the unexposed film by a notch cutter whenever the film is fed at a predetermined length. The unexposed film is wound round an exposure drum which is engaged with perforations of the film, and the latent image data is exposed on the exposure drum.
The timing for exposing the latent image data is determined as follows: the notch sensor detects a notch of the unexposed film, the perforation sensor detects a perforation and then counts the number of perforations passing, and the exposure of the latent image data is started when the count reaches a predetermined value.
In a conventional data exposure device for exposing latent image data after it detects a notch and perforations, the perforation detection accuracy varies slightly because the unexposed film flutters during feed and the exposure position may be shifted. When the exposure position is shifted, even if slightly, since the latent image data is optically exposed on the exposure drum, the exposure light interferes with, for example, a tooth of the exposure drum engaged with perforations of the unexposed film, causing an inappropriate exposure.
It is possible to detect the position of each perforation at the exposure position of the exposure drum. At this position, a reflection sensor can be used but a transmission sensor cannot. The reflection sensor cannot detect the position of each perforation stably, and a modified perforation position sensor cannot reduce variations in the exposure position.
A conventional film processing machine for manufacturing photographic roll films is provided with a latent image exposure device for exposing latent image data such as the frame numbers, side mark, side line, DX bar code, and frame number bar code on unexposed films as a dot pattern. In the latent image exposure device perforations of an unexposed film engages with the sprocket teeth of the exposure drum and the film is fed at a predetermined speed by preventing variations in the film position.
FIG. 24 illustrates the relationship between the sprocket teeth of a conventional exposure drum and perforations of an unexposed film which are engaged with them.
In FIG. 24, the exposure drum 341 has sprocket teeth 342 which are located at even intervals in correspondence with the pitch of perforations 343, and an unexposed film F is wound round the exposure drum 341 at a predetermined winding angle of .theta.. Since a tensile strength T is applied to the unexposed film F on the ascending and descending sides of the exposure drum 341, the unexposed film F is wound closely on the exposure drum 341, and the frictional force generated between the exposure drum 341 and the unexposed film F prevents the film from sliding on the drum.
In the above conventional exposure drum, the pitch "a" of the sprocket teeth 342 is equal to the pitch of perforations 343 of the unexposed film F which is set in consideration of an elongation caused by the tension applied to the film. The outer diameter D of the exposure drum 341 is obtained by calculating the theoretical length Lf of the part of the unexposed film F which is in contact with the periphery of the exposure drum 341 when the film is wound round the drum at a predetermined winding angle in consideration of the above elongation.
When the unexposed film F moves on the exposure drum 341, dot data of latent image characters stored in a control unit 344 of a latent image exposure device is read as the exposure drum 341 rotates, a light source LED in the control unit 344 selectively lights, the light is sent to a light projector 345 above the exposure drum 341 via an optical fiber, and a latent image is exposed to the predetermined film position.
As mentioned above, latent images for exposing are required to be exposed at the predetermined position of an unexposed film F with the constant size and at the predetermined position for perforations 343. FIG. 25 is an enlarged view of the latent image exposed on the unexposed film F. FIG. 25 shows a DX bar code latent image. Each DX bar code of a dot 0.095 mm in diameter, for example, is sequentially exposed to the unexposed film F at a pitch of 0.0475 mm as the film moves on the exposure drum.
When the pitch between dots for exposing is in error, the exposed graphic is deformed. The bar width d3 of DX bar codes is required to agree with the requirements 0.455.+-.0.075 mm.
So as to satisfy the above requirements, the film position near a graphic for exposing is required to be measured sufficiently accurately. However, a color film for measuring, which visible rays cannot be used for and is not physically strong, cannot be directly measured. In the conventional film position measurement, therefore, when an unexposed film F of, for example, 12, 24, or 36 exposures is used as shown in FIG. 26, a notch indicating the constant size position is cut in the unexposed film F by a notch cutter 346 under the control of the control unit 344, the notch and perforation 343 are detected by a notch sensor 348 and a perforation sensor 349 before the film is fed to the exposure drum 341 via a guide roller 347, and these detection signals are supplied to the control unit 344. The pulse number of a rotary encoder 351, which is directly connected to a rotation shaft 350 of the exposure drum 341, for generating pulses according to the movement distance of the above unexposed film F is inputted to the control unit 344, and the position is measured by using those detection signals and counting the pulse number.
So as to measure the film position highly accurately, therefore, the movement distance of the unexposed film F as the exposure drum 341 rotates is required to be perfectly synchronized with the rotation angle of the exposure drum 341 which is measured by the rotary encoder 351. When the notch cutter 346 cuts notches, however, the unexposed film F may not move uniformly. The unexposed film F is required to feed intermittently because it is cut in a predetermined length, and as a result, a pulsatory motion may occur in the feed of the unexposed film F. When the acceleration applied to the unexposed film F is larger than the angular acceleration by the frictional force generated between the exposure drum 341 and the unexposed film F and by the moment of inertia by revolution of the exposure drum 341, a match may occur in synchronization between the unexposed film F and the exposure drum 341. When such a synchronous mismatch occurs, the latent image exposure position cannot be measured correctly.
As to the relationship between the sprocket teeth 342 of the conventional exposure drum 341 and the perforations 343 of the unexposed film F, the pitch "a" of the sprocket teeth 342 is equal to that of the perforations 343 as shown in FIG. 24. Therefore, so as to prevent such a synchronous mismatch, it is required that the sprocket teeth 342 are closely engaged with the perforations 343. However, from problems such as the machining accuracy of the sprocket teeth 342 and coloration, which is called a kick, of the film caused by one of the sprocket teeth 342 touching the edge of one of the perforations 343, the maximum distance d2 of the sprocket teeth 342 is 1.75 mm for the standard distance d1 of 1.98 mm of the perforations 343. In a conventional latent image exposure device, therefore, a gap of 0.23 mm occurs between the sprocket teeth 342 and the perforation s 343, and the latent image exposure position may be shifted when a pulsatory motion occurs in the feed of the unexposed film F.